Part and product design is commonly model driven, which means that 3D modeling is employed instead of 2D drawings. This is possible, since modern CAD (Computer Aided Design) software systems support 3D design. This leads to a much more realistic representation of the final part or product compared to a 2D drawing. However, textual information is still a necessary and important complement of a 3D model to completely define a design. One important example for such textual information is dimensional tolerance. Tolerances define minimum and maximum values of a dimension. Since dimensions in a model are always single valued by nature, tolerances cannot be derived from the model but must be added separately.
PMI stands for Product and Manufacturing Information and is used to convey non-graphical information in 3D CAD Models. PMI includes dimension and tolerance, but also simple text, arrows, balloons, datum, fastener information, GD&T (Geometrical Dimension and Tolerances), measurement points, surface roughness, and welding. PMI is a standard, which is supported by all major CAD vendors, although the way how the data is represented within the CAD system is not standardized.